1. Field of the Invention
The present invention relates to a fuel cell.
2. Description of the Related Art
In recent years, attention is paid to fuel cells characterized by high energy conversion efficiency and not producing hazardous materials as a result of generating electricity. A polymer electrolyte fuel cell operating at a temperature of 100° C. or lower is known as one type of such fuel cells.
A polymer electrolyte fuel cell is a power generating device that is a membrane electrode assembly (MEA) in its basic structure in which a solid polymer electrolyte membrane is sandwiched between a fuel electrode and an air electrode. A fuel gas including hydrogen is supplied to the fuel electrode and an oxidization gas including oxygen is supplied to the air electrode. Electricity is generated according to the following electrochemical reaction.Fuel electrode: H2→2H++2e−  (1)Air electrode: ½O2+2H++2e−→H2O  (2)
At the fuel electrode, hydrogen included in the supplied fuel is split into hydrogen ions and electrons according to the formula (1) shown above. Hydrogen ions move toward the air electrode via the interior of the solid polymer electrolyte membrane. Electrons move toward the air electrode via an external circuit. At the air electrode, oxygen included in the oxidizing gas supplied to the air electrode reacts with hydrogen ions and electrons arriving from the fuel electrode, so as to produce water according to the above formula (2). As a result of electrons moving from the fuel electrode to the air electrode in the external circuit, electric power is extracted.
Separators are provided outside the fuel electrode and the air electrode. The separator outside the fuel electrode is provided with a fuel gas passage so that the fuel gas is supplied to the fuel electrode. Similarly, the separator outside the air electrode is provided with an oxidizing gas passage so that the oxidizing gas is supplied to the air electrode. A passage for cooling water for cooling the electrodes is provided between the separators.
Requirements to be fulfilled in order for a fuel cell to be commonly used at homes are small size, light weight and stable output characteristics. For this reason, studies have been made on a fuel cell stack in which fuel cells are stacked via separators (patent document No. 1). The patent document No. 1 describes an approach to improve the characteristics of fuel cell by a specific placement of passages on the plane of a separator. However, the related-art fuel cell stack has room for improvement in respect of a stable output.
Related Art List
Patent document No. 1 Japanese Laid-Open Application No. 2001-57219